This post describes the use of Format String or Control String in printf function. An example of printf function is :
printf(" [FORMAT_STRING/CONTROL_STRING] ", arg1, arg2, ... );
printf(" [FORMAT_STRING/CONTROL_STRING] ", arg1, arg2, ... );
Basic Structure of Format String or Control String in printf() Function:
% [FLAG] [WIDTH] . [PRECISION] [MODIFIER] [TYPE]
[FLAG]
- (minus)
| Output is left-adjusted within the field. Remaining field will be blank.
If no used, output is right-adjusted within the field.
Works with: char, int , float, double, string.
| ||||
+ (plus)
| The sign of the numeric will be added before the numeric value i.e. if the numric value is positive, then a + sign will be added before the value. Works with: int, float, double Prints nothing with: char, string | ||||
0 (zero)
| Causes leading zeros to appear. Works with: string, int, float, double. Prints nothing with: char | ||||
#
(with o or x)
| Causes octal and hex items to be preceded by 0 (zero) and 0x , respectively. Works with:
| ||||
#
(with e, f or g)
| Causes decimal point to be present in all floating point numbers. Prevents the truncation of trailing zeros in g-type conversion. |
Note: FLAGS can be mixed in any order
[WIDTH]
It is a +ve integer. It defines minimum field width.
Case 1: Length of data < [WIDTH]
=> Data is printed right-adjusted
Case 2: Length of data >= [WIDTH]
=> Entire data gets printed.
char str[]="world";
int a = 50;
int b = -50;
float c = 4.5446;
unsigned int d = 5;
Note: The following examples are Tested on 32 bit GCC compiler
Case 1: Length of data < [WIDTH]
=> Data is printed right-adjusted
Case 2: Length of data >= [WIDTH]
=> Entire data gets printed.
| Note: If the [WIDTH] is given as -ve, then the - (minus) sign will be treated as flag |
[PRECISION]
with String
| Indicates no of charecters to be printed . If [PRECISION] > Length of data, entire String gets printed |
with float, double and long double
| Indicates no. of digits to be printed after decimal point. If [PRECISION] < no. of digits after decimal point, rounded value will be printed. If [PRECISION] > no. of digits after decimal point, trailing zeros will be added. |
with integer
| If [PRECISION] > Length of data, prints (precision - length of data) no. of zeros. |
with char
| Does nothing |
| Note: [PRECISION] is a positive integer. If it is given as negative, then - (minus) sign + precision value + type gets printed. |
[MODIFIERS]
h
| for short integer |
l
| for long integers or double |
L
| for long double |
[TYPE]
%a
| Hexadecimal output in the form 0x h.hhhhhh p+ or - xxxx (C99 only) |
%A
| Hexadecimal output in the form 0x h.hhhhhh P+ or - xxxx (C99 only) |
%x
| Hexadecimal integer e.g. 0x5fc8 |
%X
| Hexadecimal integer e.g. 0x5FC8 |
%o
| Octal integer e.g. 0879 |
%c
| type char e.g. 'a', 'A', '8' etc. |
%d
| decimal integer (signed ) e.g. 5, -4 etc. |
%i
| decimal integer (signed ) e.g. 6, -6 etc. |
%u
| unsigned decimal integer etc. 5, 6 etc. |
%s
| String e.g. "Do you like this article?" etc. |
%e
| scientific notation in the form d.xxxxxx e + or - xxx |
%E
| scientific notation in the form d.xxxxxx E + or - xxx |
%f
| float in the form d.xxxxxx e.g. 5.000000 |
%g
| uses %e or %f whichever is shorter e.g. 100000, 1e+006, 0.0005, 5e-005 etc. |
%G
| uses %E or %f whichever is shorter |
%p
| Segment address (of pointer variable) in Hex. e.g. 12ao |
%Fp
| Segment address and offset address in Hex. e.g. 0001:00f2 |
%n
| The associated argument must be a pointer to an integer. This specifier causes the number of charecters written (upto the point at which %n is entercounted) to be stored in that integer. |
%%
| prints a % sign |
| Note: [WIDTH] and [PRECISION] can be specified as a argument variable in printf() function. For example, printf( "%*.*s" , width, precision ); |
Few Examples of printf() Function
Assume, the following variable declarations:char str[]="world";
int a = 50;
int b = -50;
float c = 4.5446;
unsigned int d = 5;
Note: The following examples are Tested on 32 bit GCC compiler
Statements
| Output |
printf("%s", str);
printf("%-10s",str);
printf("%2s",str);
printf("%-2s",str);
printf("%(-10)s",str);
printf("%-(-10)s",str);
printf("%20(-10)s",str);
printf("%5s",str);
printf("%-5s",str);
printf("%+10s",str);
printf("%010s",str);
| world world world world (-10)s (-10)s (-10)s world world world 00000world |
| printf("%-10d",a); printf("%+-10d",a); printf("%010d",a); printf("%0+10d",a); printf("%+0+10d",a); printf("%010d",b); printf("%#d",a); printf("%#x %x",a,a); printf("%#o %o",a,a); printf("%f",6); printf("%f",6.); printf("%f",6.0); printf("%f"); printf("%d"); | 50 +50 0000000050 +000000050 +000000050 -000000050 50 0x32 32 062 62 0.000000 6.000000 6.000000 0.000000 garbage value |
| printf("%10.2s",str); printf("%10.8s",str); printf("%10.-4s",str); printf("%1.-4s",str); printf("%10.5f",c); printf("%10.3f",c); printf("%10.9f",c); printf("%.5f",c); printf("%4.3d",a); printf("%.0d",a); printf("%d %d", 5, -5); printf("%i %i", 6, -6); printf("%u %u", 7, -7); printf("%5.3c",'d'); printf("%0c",'d'); printf("%I64"); printf("%s","Hello"); printf("%s","%d",5); printf("I64d",5); printf("%I64d",-5); printf("%d"+1,5); | wo world -4s -4s 4.54460 4.545 4.54600000 4.54460 050 50 5 -5 6 -6 7 4294967289 d d prints nothing Hello %d 21474836485 25769803771 d |
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